The scalar-electromagnetic couplings make the Kaluza theory unique among scalar-tensor theories, and markedly different from Brans-Dicke theory. The Kaluza Lagrangian (REF ) contains aspects of the Brans-Dicke scalar-tensor Lagrangian [1]}, [2]}. In each case, the scalar field can be viewed as a variable gravitational constant. The Kaluza Lagrangian also contains aspects of the Bekenstein scalar-electromagnetic theory [3]}, with a variable vacuum permittivity, although Bekenstein did not start from a Lagrangian, and spoke in terms of a variable fine structure constant.
